This invention relates to apparatus for wiring electrical circuits and more particularly to an improved modular breadboard for temporarily mounting and interconnecting electrical components to form an electronic circuit.
Newly designed and experimental electrical circuits commonly are tested by temporarily constructing the circuit on a breadboard. Generally, circuit elements are either mounted directly on the breadboard or attached to the breadboard by means of lead wires which are connected to terminals mounted on the breadboard. Two basic types of terminals commonly are used on prior art breadboards. On one type of terminal, connections are made by soldering circuit component leads and wires interconnecting circuit components to terminal posts. Solder terminals are relatively permanent and the connections will withstand considerable vibrations and other stresses before failure. However, it is time-consuming and difficult to change circuit connections when the circuit or a circuit component is modified. Considerable time is also required to disassemble the circuit after it is tested and no longer needed if the circuit components are to be salvaged. A second type of terminal, which is solderless, releasably holds component leads and wires to facilitate rapid circuit assembly, rapid circuit modification and rapid circuit disassembly after the circuit is tested and no longer needed. Typical solderless terminals are shown, for example, in U.S. Pat. No. 3,150,911 which issued to Matteson on Sept. 29, l964 and U.S. Pat. No. 3,564,480 which issued to Dziubaty on Feb. 16, 1971. These patents disclose solderless terminals consisting of a helical tension spring mounted in a housing. The housing either is stamped to form four upstanding fingers which are spaced around the spring or is molded from a synthetic resinous material. When an outer end coil on the spring, which forms a handle, is pulled, the spring coils are separated to receive wires and/or circuit component leads. The handle is then released and the spring retracts to clamp onto the wires and/or component leads, thereby completing the circuit.
Prior art terminals suitable for use on breadboards are connected to breadboards by various methods. The solderless terminal shown in U.S. Pat. No. 3,150,911 is assembled and attached to a breadboard by means of either a woodscrew or a bolt passed through an inner end coil of the spring and the retainer housing. The strength of the bolt or screw is limited since the head of the bolt or screw must fit within the spring and housing. This in turn limits the strength of the attachment between the terminal and the breadboard. Another type of terminal has an end adapted to be pushed into a hole drilled into the breadboard. This type of terminal typically is held in place either by friction with a press fit into the hole or with one or more detents formed on the terminal for engaging the breadboard.
When constructing circuits on a breadboard, it sometimes is desirable to use prewired circuit modules containing circuit subassemblies such as an amplifier circuit or circuit components such as sockets for integrated circuits, transistors, tubes, relays and the like. U.S. Pat. No. 3,514,872, which issued June 2, 1970 to Bradley, discloses a breadboard assembly having a grid of spaced electrically conductive terminals. Rectangular circuit modules are positioned between and electrically contact four of the terminals located on the breadboard for cooperating with terminals on the corners of the modules. This arrangement permits rapid connection of the modules to the breadboard in constructing a circuit. However, only a limited number of circuit connections may be made to a module since each rectangular module has only four terminals. Furthermore, connections are made only between adjoining modules since there is no provision for connecting wires to the terminals. U.S. Pat. No. 3,633,074, which issued Jan. 4, 1972 to Nojiri, shows a similar breadboard construction in which terminals on circuit modules plug into openings in a board. Electrical contact is made between such terminals and abutting terminals on adjacent modules inserted into the same openings. The breadboard constructions disclosed in both of these patents are suitable only for assembling relatively simple circuits having a limited number of connections.